Arsenal players will be "spoken to" by club chiefs after images emerged allegedly showing four members of the first team inhaling nitrous oxide.
Arsenal players have been filmed at a "wild champagne and vodka party" that took place the week before the season, with Mesut Ozil, Alexandre Lacazette, Pierre-Emerick Aubameyang, Sead Kolasinac and Matteo Guendouzi all appearing to inhale "hippy crack" from balloons.
An Arsenal spokesperson told the BBC players would be "spoken to and reminded of their responsibilities".
It can make users feel euphoric and relaxed, with some reporting hallucinations, and can lead to loss of blood pressure, fainting and even heart attack.
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Nitrous oxide, also known as laughing gas or "hippy crack", is freely available although it is technically illegal to sell it for recreational purposes.
Arsenal lost their first two matches of the season against City and Chelsea but have not been beaten since and are now on a run of 20 games without suffering a defeat.
In the same year, Jack Grealish was warned by the then Aston Villa manager Tim Sherwood after pictures emerged of him appearing to inhale the gas, and Saido Berahino was reprimanded by West Brom for a similar incident in 2014.
The use of nitrous oxide in balloons has becoming increasing popular at parties.